It's also a timely metaphor, because the color of snow is actually changing across the globe, including in the West. The phenomenon is attributed to various human activities and carries big implications for everything snow-related, including skiing, farming, forest health and municipal water supplies.

The latest example comes from southwest Idaho, where March winds transported a layer of desert dust onto the snowpack at an Owyhee Mountains research station. Snow surveyors over 60 miles away also observed the dusty snow. Dust absorbs heat and can be ruinous for snowpacks. During the following 10 days, research cameras showed accelerated melting that contributed to an early runoff in local rivers - a big deal for farmers, rafters, fly-fishers, fish and wildlife. Scientists blamed the event on exceptionally dry conditions in the Great Basin desert.

Water specialists told the Idaho Statesman they'd never seen anything like it. But in Colorado, I remember the umber-colored snowstorm the day after Valentine's Day, 2006, during one of my last winters in the high country. Weather observers reported dusty snow from Durango to northern Colorado, across over 100 miles of mountains.

The dust stained every mountain face and plagued the snowpack for the rest of the winter. It happened again in 2009, leading some snowpacks to melt 48 days early, according to University of Utah researchers. Scientists tied these events to drought conditions as well: an abnormally dry desert Southwest.

Dust kills snow dead. It reduces the reflectivity that keeps snowpacks cool. Its dark particles also absorb heat, further warming snow. And the accelerated melting uncovers vegetation and soil, revealing dark surfaces that absorb additional heat and melt more snow. With snow producing up to 75 percent of water for many Westerners, and climate change already diminishing Western snowpacks, the events are causing alarm.

Research adds to concerns. Satellite imagery and analysis of dust confirms its origins in U.S. deserts. In Colorado, researchers using pond sediments created a 5,000-year dust-deposition record that showed dramatic increases in the late 1800s, synchronous with the arrival of hordes of settlers with herds of cattle, which destabilized soils.

Current dust deposition remains 500 times pre-settlement levels, and contributors to the problem include grazing, development, off-highway vehicles, and drilling.

The impacts are felt high in the mountains and follow rivers downward, from ski areas to reservoirs, farms and cities - all the way to thirsty Los Angeles. One researcher estimates dust on snow reduces the Colorado River's flow by 5 percent, stealing enough water to supply Los Angeles for 18 months.

Pollution is also changing the color and impact of snow. Department of Energy research shows soot from coal-fired energy plants and diesel engines causes widespread snowmelt in the Cascades and Rockies. This reflects a growing global threat to snow and ice. Industrial soot travels far and increasingly is blamed for the rapid melting of Arctic sea ice and Alaska's incredible shrinking glaciers. Asian coal-fired energy plants enhance melting in the Himalayas. Meanwhile, millions of wood-burning stoves in Africa launch additional soot into the atmosphere, to be later carried Earthward by faraway snows. In Greenland, researchers tied melting to soot from fires in the Alaskan Arctic.

Here in the American West, scientific models show a hotter, drier region with less vegetation and more dust. In both Idaho and Colorado, abnormally dry desert conditions contribute to dust-on-snow events. Increasing forest fires, including last summer's blazes downwind of the Owyhees, can also remove vegetation and destabilize soils. In the Arctic, increasing fires produce soot destined for sea ice and globally significant ice caps.

The implications are wide-ranging. For instance, if off-roading and drilling are sending dust aloft from increasingly arid deserts, it lends ecological credence to long-standing proposals to designate some of Utah's BLM lands as wilderness, places where the dust itself can remain undisturbed. And if soot from Asian coal plants is dirtying snow and melting glaciers, including on our own continent, it undermines the economic argument for building enormous coal export facilities in Washington. This new world we're in also makes the December 2012 decision to strengthen Clean Air Act soot standards - lambasted by Republicans as "job-killing" - look like a good idea. The same goes for the multi-national initiative to reduce soot that was announced last year by then-Secretary of State Hillary Clinton. In these and other examples, seemingly distant policy decisions have a bearing on snow and the people who rely on it, including here in the West.

Tim Lydon is a contributor to Writers on the Range, a service of High Country News (hcn.org). He writes from south-central Alaska.